The present invention relates to servo valves and more particularly to an electro hydraulic rotary servo valve that is adaptable to be used with high speed drives of sheet fabricating machines.
Servo valves are usually associated with spool type valves that are used to control the flow of fluid, such as hydraulic oil or air, to a hydraulic cylinder or similar drive devices. The flow capacity is usually determined by the size of the spool, and the amount and rate of the flow of fluid are usually determined by the position of the spool relative to the valve body, or housing, to which the spool is movably fitted.
A servo valve acts as an interface to permit low energy electrical signals to manipulate high level hydraulic power. There are generally three types of electrically operated servo valves. They are proportional, directional flow and pressure control. A conventional servo valve is a four port unit that has its spool movable axially along the length of the valve body so that the fluid flow controlled by the valve is in proportion to the spool displacement. And the displacement of the spool is in proportion to the electrical signal applied, thereby enabling the control of the rate of fluid flow, as well as the direction of the fluid flow.
There are a number of conventional servo valves being sold. One of such servo valves is made by the Parker Hannifin Corporation of Elyria, Ohio under their series designation BD. Another servo valve that is used with the hydraulic system of a sheet fabrication machine is made by the Bosch Company under the designation HRV1. Such Bosch valve has its spool movable axially inside the valve body for controlling the flow and rate of hydraulic fluid. There is also disclosed in U.S. Pat. No. 5,954,093 a servo valve that, instead of having an axially movable spool, utilizes a double edged metering blade that is movably mounted to a sleeve fitted inside the bore of a servo valve body, which is divided into a number of spaced apart annular chambers. The fact that the ""093 device requires a valve body that is predefined into a number of chambers, the fitting of a sleeve into the valve body and the fitting of a double edged blade within the sleeve mean that the construction of the ""093 device is quite complicated, and expensive. A similar rotary servo valve that also requires a multi-chamber valve body, a sleeve fitted within the bore of the body, and a rotating member fitted within the sleeve is disclosed in U.S. Pat. No. 5,467,800. The member that rotates within the sleeve of the ""800 device in turn is separated into two closed internal chambers. A published Japanese patent application (11-107134) discloses a servo valve to be used with a turret punch press that has a spool that is movable both axially and rotationally. To enable both axial and rotational movement, both a linear actuator motor and a rotational servo motor are used. Needless to say, such dual motor servo valve is expensive.
A need therefore exists for an uncomplicated and inexpensive electro-hydraulic servo valve that is adaptable to be used with the high speed drive system of a sheet fabrication machine.
The electro hydraulic servo valve of the instant invention has a valve body or housing that has at least two sets of ports formed along the length of the body offset from each other. A hollow spool or cylinder is fitted inside the bore of the housing. A number of orifices are formed along the length of the spool. The orifices are positioned along the spool such that when the spool is rotated a certain distance, selected ones of the orifices become aligned with corresponding ports of the valve body. The hollow cylinder, in addition to having the orifices formed along its length, also has an open end through which fluid, hydraulic or otherwise, passes. A fluid passage is established between the open end of the cylinder and the driving mechanism of the sheet fabrication machine or system.
The other end of the spool extends out of the valve body and is connected to a servo motor. The motor rotates the spool in accordance with instructions from a processor, which may be a component of the sheet fabrication machine.
The valve housing is made up of an aft section and a fore section. Corresponding ports are provided at each of those sections. The ports at the aft and fore sections are configured to be offset from each other. Those ports in turn are coupled to appropriate conduits. One of the conduits that is coupled to one section of the valve housing is connected to a fluid reservoir or sink to which the hydraulic fluid is stored. Another of the conduits that is coupled to the other section of the valve body is connected to a pump, which pumps the hydraulic fluid from the reservoir. The open end of the spool which forms the fluid passage in turn is connected to forward and return conduits that are in fluid communication with the hydraulic cylinder of the drive mechanism, which may be a piston connected to a ram. By selectively rotating the spool relative to the valve housing, selective fluid paths may be established for pumping the hydraulic fluid to the hydraulic cylinder to drive the ram downwards, or for returning the fluid pumped into the hydraulic cylinder to the hydraulic oil sink to thereby raise the ram. By thus simply rotating the spool relative to the valve body to drive the ram, the servo valve of the instant invention is capable of effecting the bidirectional movement of a fluid at a much greater speed and higher efficiency than conventional servo valves. The movement speed or work cycle of the ram, which is being driven by the servo valve, accordingly is increased.
It is therefore an objective of the present invention to provide a servo valve that operates at a greater speed than conventional servo valves.
It is yet another objective of the present invention to provide a servo valve that is less expensive to construct and simpler to use than conventional servo valves.
It is yet another objective of the present invention to provide a servo valve whose work cycle can be increased, and therefore whose work efficiency is higher than conventional servo valves.